Numerous man-made composites and natural materials are known for myriad uses, including exterior applications. For example, aromatic polyurethane is used in applications ranging from foam for car seats and bedding to rigid applications; the range of products made with this type of technology is vast. Exterior use of aromatic polyurethane, as well as other materials, has been limited due to degradation and discoloration upon exposure to ultra-violet light. Over time, ultra-violet light causes a radical reaction in aromatic polyurethane that breaks down the aromatic portions of the polymer, causing a severe yellowing of the substrate. In order to make an exterior product comprised mainly of aromatic polyurethane, or other materials susceptible to exterior conditions, it must be coated in such a way as to prevent ultra-violet light from reaching the substrate.
Coating composite materials for exterior use to look like wood has been carried out by various processes. Some composite materials are encapsulated in a cap-stock; this cap-stock is generally a thermoplastic type material that can be extruded. The look of wood is generally achieved by some type of embossing, in which the wood grain is three-dimensionally represented. The color variation is generally achieved by the incorporation of various colors during extrusion or pultrusion.
Coating of plastics has been achieved with a wide variety of techniques, some of which are used during the process described herein. A few techniques include, but are not limited to, general spray techniques such as high-pressure and low-pressure systems, roll-coating methods, powder coatings, hydrographics, and UV-curable coatings. Some manufacturers rely on the three dimensional wood-grain and a solid color, while others will work to add a variety of colors to the substrate using methods such as printing to achieve a wood-like appearance.
Described herein is a process by which aromatic polyurethane, for example, can be coated with a fully hiding coating which has been proven to protect the substrate while creating the appearance of wood by combining general techniques in a unique process to promote adhesion, while creating the desired wood-like appearance.